Containers, such as bottles, are often used to contain liquid, for example beverages. The containers can be produced from a transparent or translucent material, for example glass or a translucent plastic material, e.g. PET, or also from sheeting. In the course of container processing, containers are supplied to a filling system, in which they are filled with a liquid product, and once filled, closed.
As the containers are being filled, it must be ensured that each container is filled with the necessary quantity of liquid product according to standard default settings, and that the container is not over-filled with an excessive quantity.
Carrying out a fill level check is a known way to ascertain whether the container is filled with the necessary quantity of liquid product. In this case the respective containers run through an inspection device, that illuminates the containers e.g. in the region of their bottle neck, as an example, and records the corresponding data, e.g. by means of a CCD camera. In an evaluation-and-control unit the actual data recorded is compared with required data such that under-filled or over-filled containers can be separated out. It is important also that this inspection not be carried out in a random manner, but that each container be correspondingly checked. Sensor arrangements with transmitters and receivers are also known in connection with this application.
It is also known, for example, that carbonated liquid products are foamed up in order, once air has successfully been displaced from the container head space, to achieve closing of the containers. This avoids impairment of the liquid product by oxygen inside the closed containers. It is naturally conceivable that liquid products that have not undergone any particular foaming-up procedure are also subject to the formation of foam.
A difficulty that arises is that the foam can confuse an optical sensor. As a result, under-filled or over-filled containers could be deemed to have the correct fill level even though they do not. The converse error is also possible. In some cases, correctly filled containers are rejected. In addition, the containers, for example bottles, are subject to certain shape tolerances such that could also result in an unreliable inspection result.
One way to avoid these difficulties is to weigh the filled containers. To do this, the individual containers are removed from the container flow and weighed, one at a time, by a separate holding device. Once the specific weight of the liquid product and the weight of the empty container are known, it is possible to deduce the filled weight. If the weight is too high or too low, the container is separated out.
The main disadvantage with this approach is the need to interrupt container flow to weigh the containers one-by-one. This is a significant disadvantage in modern filling systems that nowadays have throughput on the order of 60,000 containers per hour. Any interruption in the container flow results in considerable time losses and consequently in economic losses.
DE 103 01 844 A1 discloses a filling machine that relies on weighing. The described apparatus initially weighs the empty containers. After filling them, it weighs them again. To achieve this, the supplying conveyor comprises two parts, between which scales are located. The containers are moved from the first part of the supplying conveyor onto the scales by suitable means that are not actually explained in detail. As described above, the containers are certainly raised by means of a holding device and placed onto the scales in order, after weighing, to transfer the containers in the very same manner to the second part of the supplying conveyor. However, this certainly interrupts the container flow. The weighed empty containers are filled by means of filling devices and are then removed by way of a removal conveyor. The removal conveyor, analogous to the supplying conveyor, is formed by two parts, between which a second set of scales is located for weighing the filled containers. In this case too, it appears that the respective container is moved to the scales by means of separate holding devices, and is then removed again. This interrupts container flow yet again.
In order to achieve a measurement at a high conveying speed without interrupting container flow, DE 103 01 844 A1 consequently proposes that individual containers be transferred out of the container flow. The transferred-out containers are supplied to a measuring point located next to the removal conveyor. This means, however, that it is no longer possible to check the fill quantity of each container in a continuous manner. Instead, fill quantity is checked in a random manner.